I have been thinking about putting my carbine upper with an A2 stocked lower I have. I am taller (6’1") and the A2 fits me to a tee. Will the carbine length upper be a problem with a rifle length buffer tube though? Do I need a different buffer or spring as I have the original rifle buffer and spring installed. I looked this up with the search feature and it told me that the search had too many common words. Thanks again for all the help guys!
I have ran them like that off and on for years without any issues. Kyle Defoor used to run a carbine upper on a A1 or A2 lower when he was still teaching at Blackwater and it never seemed to give him any issues.
I just use a standard rifle receiver extension, rifle buffer and spring.
Thank you, I just wanted to be sure. I had heard from an unreliable shop employee that this was a no-no. I swore that I had seen this done before at least in pics and videos but he said I was wrong. He also said I would damage the buffer tube. I thought this seemed like bull because I wasn’t changing the shape of the bcg. I just wanted to make sure that the ARs in the pics weren’t being run different springs or buffers.
Being 6’5" I run the same a mid-legnth set up on my RRA riflr lower, and have not had an issue. I have also observed numerous carbine uppers on Riflr lowers without a problem.
If it wasn’t for the mis informed we wouldn’t be asking these questions. 
I’ve run a couple LE6920 uppers on my MK12 lower with an A2 stock. Never had any problems doing. I liked the feel I got from the A2 stock in regards to LOP.
It will run better.
Try this thread for more info:
http://m4carbine.net/showthread.php?t=98092
(I thought I recognized markm’s rifle!)
Thanks guys! Damn, that is a pretty AR Markm! I was wondering what it would look like. I can’t wait to get my extra stock assembly from PSA! I like the A2 on my A4gery and had to leave it alone, I don’t like the carbine stock one bit. I can’t wait for the Magpul MOE fixed stock to come out.
Use the original rifle buffer spring and buffer.
ETA: The receiver extension dictates which length spring and buffer you use. Both the A1 and A2 use the same rifle extension and require a rifle buffer and spring.